Don't shave the arm. See if you can get the ball out of that broken shock end. They are a bit tricky to get out, but a pair of pliers and a small wrench that spans the ball on one side usually works for me. Clamp the pliers on the ball on one side, and on the wrench on the other.
By the way...
Well kiddo, you are kicking butt in this hobby for a 12 year old. My son is 9, and by the way, he wanted me to send you a message on one of your latest Roblox vids to add him on Roblox 😉 I used his channel to send you the message - Breydon's RC Channel. He is getting ready to do another unboxing...
Try what Grey said. That should work if the balls are the same size.
How old did you say you were David?
If the balls are different size, you could cut the flange down with a rotary tool. I have had to do this a few times. What I did was clamped the ball in a drill chuck and spun the drill...